The classification of the South Asian river dolphin continues to be hotly debated in scientific circles. Originally thought to be the same species, the Indus bhulan and Ganges susu were listed as separate species in 1971 due to apparent differences in skull structure and blood proteins. However this speciation has never been fully accepted and currently the two populations are recognised as subspecies of the species Platanista gangetica; those found in Nepal, India and Bangladesh are classified as P.g. gangetica while those found in the Indus River in Pakistan are known as P. g. minor.

Appearance:

This dolphin has a distinctively long slender beak with sharp, pointed teeth. Proportionally longer in females than in males, the beak is designed for quick snapping action to capture fast prey. It has a prominent melon and, unlike most cetaceans, the cervical vertebrae of the South Asian River dolphin are not fused, allowing it to flex its neck. It has broad paddle-shaped flippers, a stocky body, a small triangular dorsal fin, and its fluke is broad with pointed tips. The colouration of the South Asian river dolphin is variable, ranging from chocolate brown or tan to greyish or pale blue, with the belly paler than the rest of the body. The eyes are small, lack a crystalline lens and are almost useless, though vision isn't very effective in cloudy estuary habitats. They may be able to sense light intensity and direction but not distinct shapes. While several other species overlap its range and are often confused with Platanista, it is physically unique and relatively easy to identify in the wild.

Behaviour:

Both subspecies of South Asian River dolphin are generally found alone or in pairs, and occasionally in small groups. Little is known about their behaviour as they tend to be elusive, fast moving and shy of boats. They are not demonstrative or acrobatic but when distressed, they may breach, though this is a rare behaviour. P.g. gangetica's habit of surfacing at a steep angle with its beak and head sticking out of the water often causes it to be confused with the gharial, a type of crocodile also found in the Ganges River and tributaries. These dolphins sometimes gather in counter-current pools near channel convergences, sharp meanders and human-built structures that cause similar effects. These features probably help to concentrate their prey.

Distribution:

P.g. gangetica is found in the Ganges-Brahmaputra-Meghna and the Karnaphuli-Sangu river systems and their tributaries, while P.g.minor is found only in the Indus River. Due to their riverine habitats, both face threats from human activities although to different degrees. (1) P.g.minor - Barrages or dams have segmented their traditional range, fragmenting the population of the Indus susu. Much of its range is not habitable year round due to fluctuating water levels and recent increases in demand for water and problems with drought further reduce their range. In the dry season, many individuals become trapped in irrigation canals. Other threats include habitat destruction and degradation, entanglement in nets and fishing gear, and pollution. (2) P.g. gangetica - Although now greatly reduced, there is some deliberate, illegal killing of Ganges river dolphins. They are taken due to the perceived fisheries competition, the value of their oil in traditional medicines, as bait, and for food. Other threats include increased growth of aquatic plants and chemical pollution. More significant, however, is accidental capture in fishing operations, especially gillnets. Gaining accurate population data is difficult for this species but it is clear that numbers are small and that its range is greatly reduced. In the case of the Indus susu its historical range has been reduced by up to 80%. Fewer than 1,000 individuals are thought to remain in the Indus River and double that in the Ganges and associated rivers. The species is listed by IUCN as Endangered (2008).